1. Field of the Invention
The present invention relates to a method of manufacturing phenols by thermal decomposition of lignin, which is a main ingredient of plant body of wood, bamboo or straw and is obtained as a by-product of paper, pulp production process.
In the chemical pulping process using sulfur-containing-compounds or alkali materials as a lignin-removing agent, lignin obtained as a by-product therefrom is generally burnt up without utilizing it in an effective way.
2. Description of the Prior Art
In Japanese patent public disclosure Tokkaisho 59-163495, a manufacturing process of pulp has been proposed wherein lignin is removed from wood or ligno-cellulosic materials by heating it in a liquid medium consisting of phenols or a mixture of phenols and glycols, and a mixture of water and acetic acid. In this process, it is suggested to make use of phenols obtained by a thermal decomposition or a hydrogenation-decomposition of lignin or a mixture of lignin and hemicellulose formed during the lignin-removing process as aforementioned liquid medium consisting of phenols or a mixture of phenols and glycols. However, no detailed description of conditions for thermal decomposition or hydrogenation-decomposition of lignin or a mixture of lignin and hemicellulose was shown in Tokkaisho 59-163495.
A method is known for manufacturing phenols by hydrogenation-decomposition of lignin, wherein lignin obtained from the residue of wood-saccharizing was treated with hydrogen in the presence of copper-chromite, Co-Mo/diatomaceous earth, Ni-carbonyl or Fe-carbonyl catalyst in a solvent of cyclohexanol at 60-100 kg/cm.sup.2 G and 380.degree.-400.degree. C. for 0.5-2 hours J. Japan Wood Res. Soc. Vol. 7, page 19-23, (1961); Bulletin of the Government Forest Experiment Station, No. 151, page 137-153, (1963); and Bulletin of the Government Forest Experiment Station, No. 166, pages 159-171, (1964).
However, it has been difficult to obtain phenols effectively by only thermally decomposing lignin (cf. comparative examples described later), and no commercial process of manufacturing phenols by thermal decomposition of lignin has been developed so far.